In the automotive art, it can be desirable to monitor the rotary position of an engine throttle shaft as an input operating parameter to an engine control module. In the prior art, typically the lever arm of a variable-voltage sensor has a hub having an axial bore including an internal flat that is slipped onto the end of a throttle shaft provided with a mating external flat, such that the hub, once installed onto the shaft, cannot rotate independently of the shaft. Typically, the mating of the hub to the shaft is deliberately slightly loose to facilitate assembly and to allow for stack-up of manufacturing variances in the various components. In modern engine control, however, the resulting rotational play between the hub and the shaft can be unacceptably large, leading to imprecise determination of the actual position of the throttle shaft and hysteresis in the control loop.
A further disadvantage of this connecting scheme is that the rotary relationship between the throttle shaft and the sensor is fixed for all throttle shafts and sensors by the design placement of the flats and does not allow for individual, independent calibration of throttle flow and sensor output on any given engine prior to fixing the rotary relationship between the shaft and the sensor.
It is highly desirable to be able to set the throttle position at a predetermined air flow and to independently set the sensor at a predetermined output after the sensor hub has been slipped onto the throttle shaft, and then to immobilize the indexed relationship by securing the sensor hub to the throttle shaft. Such immobilization by prior art means can be expensive, as in for example the case of laser welding or a set screw or adhesives, and/or can jeopardize the delicate rotary relationship just established, as in the case of staking or crimping of the hub onto the shaft.
Therefore, there is a strong need for a simple, inexpensive, reliable means for immobilizing a hub onto a shaft without inducing rotational forces therebetween, while previously allowing relative rotary motion therebetween as may be necessary to index the hub to the shaft.
It is a principal object of this invention to provide an improved apparatus for immobilizing a hub onto a rotatable shaft without inducing rotational forces therebetween, to cause fixed rotation of the hub and shaft together, while allowing relative rotational motion therebetween prior to such immobilizing, as may be necessary to index the hub to the shaft.